Return to Ravnica (the most recent MTG expansion) had a return of 150%+ ... which is out of the norm... some large dealers were bringing very close to 200% returns. Of course this is all within the first few weeks of release then aggregate prices go down somewhat.

With MTG, sets are hit or miss and many times box/cases jump in price as soon as it's realized the set is "loaded." But the game is very strong right now and lately there have been some great sets.

However looks like mostly thanks to Return to Ravnica, presell box/case prices are inflated somewhat so becareful. If you have a brick and mortar store and fill out the paperwork, you can get "dealer" prices which is the best way to maximize profits and cushion yourself from inflated presell sealed product prices.